Black as night I can be, Until my Mother sits on me; Then clear as ice I become In the rough, thank you Mum. What am I?

Question

I am black as night but filled with light. I can be seen, even through a screen. I hold many secrets, waiting for them to be discovered. What am I?

Answer 1

Coal

When buried deep in Mother Earth, the high pressure transforms black coal into clear diamonds; a diamond in the rough.